The goal of this project is to elucidate the cellular and molecular mechanisms regulating the formation of synaptic connections in the vertebrate central nervous system. To this end we will analyze the development of synaptic connections between hindlimb muscle afferents and lumbosacral motoneurons in the chick embryo. Intracellular recordings from motoneurons of 20 day old embryos will be obtained using an isolated cord preparation to determine the qualitatively mature pattern of connectivity between specific muscles and particular motoneuron pools. This information will allow us to establish if the first sensorimotor connections that form are appropriate and to assess the effects of experimental manipulations on the development of connectivity. We will then determine if synaptic transmission between sensory neurons and their central targets is required for the formation of appropriate sensorimotor connections. In addition, we will test the hypothesis that the naturally occurring death of sensory neurons eliminates erroneous sensorimotor connections. We will do this by establishing if abnormal connections follow experimental reductions in sensory cell death. Finally, a chronic in vitro preparation of the embryo will be developed that will be used to assay the formation of sensorimotor connections as they develop under rigorously defined environmental conditions. This preparation will be used as an adjunct to the in ovo preparation for chronic antibody and pharmacological manipulations. The second part of the project will continue our work generating and characterizing monoclonal antibodies that recognize antigens on sensory and motor neurons. We are particularly interested in finding surface molecules whose expression is developmentally regulated since these may be involved in the formation of sensorimotor connections. The role of the antigens in the development and function of sensorimotor connections will be assessed in two ways. First, by manipulating sensorimotor pathways and establishing if this alters the expression of the antigen. Secondly, by using the antibodies to perturb the development and function of sensorimotor connections.